Simulation of Human Processing of Information

and ask him to fill in the next letters. Most students will rather quickly reply with the letters FMGHM . Next, give the starting sequence DEFGEFGHF * * . This time there will be a longer pause before the reply. Some, but not all, the students will presently propose GHIGHIJ ... as the continuation. Occasionally, a mathematically talented student, when presented with such problems, will reply that any letter is a legitimate continuation of any starting sequence. When we encounter such a student, we will compliment him on his acumen, and then pose a new kind of problem to him. We will point out to him that in fact, subjects presented with such sequences do not reply with "any" letter, but show a high degree of consensus as to what the "right" next letters are. Moreover, the sequences can clearly be ranked according to difficulty, on the basis of how much time subjects take to answer, and on the basis of how many find the "right" answer. Finally, subjects who score high on tests of general intelligence, and particularly on tests of mathematical aptitude, are more likely to give the "right" answers than subjects who score low on such tests. Hence, if the problem we have posed is ill-defined from a mathematical standpoint, it raises a perfectly well-defined problem for psychology: how do human beings perform tasks like this one? What processes do they carry out, how do they find an answer, how do they judge it correct, how do they produce the extrapolating letters? Psychology needs a theory to explain behavioral phenomena like these; it needs a formal language for stating the theory; and it needs techniques for testing the theory empirically.